a. Field of the Invention
The present invention pertains generally to redundant data storage systems and more specifically to the restoration of replaced or repaired storage units in redundant data storage system.
b. Description of the Background
Several types of redundant data storage systems are in use today. RAID systems, which use several independent disk drives, may be configured in several different manners so that if one of the disk drives fails, the data is not lost. Such systems have been developed because of the often catastrophic and unannounced failures of disk drives.
Other types of redundant data storage systems have been developed. In one solution, remote mirroring systems may maintain two identical data storage systems at remote locations. In such a system, one data storage system may be located in one location and an identical copy, or mirror, may be located in a different location, such as another building, state, or country.
Redundant systems of the type described above often allow for a single disk to be removed and replaced. Sometimes, such replacement may be performed ‘hot’ or when the system is otherwise up and running. When the disk is replaced, various methodologies may be used to restore the data onto the new disk. In the example of a RAID 1, or mirrored disk system, when one disk is replaced, the data is copied from the good disk to the newly replaced disk. In an example of RAID 5, the data on the replaced disk is recovered by recreating the data from the stored parity.
Recovering or rebuilding a lost disk drive or other data storage subsystem becomes problematic as the size of the disk drive or data storage subsystem increases. As the disk drive becomes large, the amount of time required for rebuilding likewise increases. During the rebuilding process, the data storage system is most vulnerable to an additional failure, since the redundancy may not exist until the rebuilding process is complete. Further, the controller and disk drives tend to be busy with the rebuilding process which causes the system response time to read and write requests to become a problem.
It would therefore be advantageous to provide a system and method for quickly rebuilding a replaced or serviced data storage unit in a redundant data storage system. It would be further advantageous if such a system minimized the amount of time that the system would be vulnerable to additional problems and be operating at a reduced performance.